Field of the Invention
This invention relates to methods and apparatus for producing a disk rotor used e.g., for a vehicle braking device.
The disk rotor, used for a disk brake, is conventionally manufactured by casting (gravity casting). Since there is a demand nowadays for a lightweight vehicle, attempts are being made to use aluminum in preference to cast iron so far used, such that researches and developments are going on briskly.
Meanwhile, if the disk rotor is manufactured from aluminum by itself, there is raised such problem as low mechanical strength or susceptibility to wear. For overcoming this inconvenience, such technique has been developed which makes use of a ring-shaped pre-form obtained on solidifying e.g., alumina particles under pressurization or sintering. In manufacturing a disk rotor employing such pre-form, molten metal (molten aluminum) is forcively charged into a cavity defined by metal molds (or dies), as the pre-form is supported at a preset location in a metal mold. Since the molten metal is impregnated into micro-sized pores of the pre-form, a molded product, in which the pre-form and aluminum are unified together, is obtained on solidification of the molten metal. The portion of the disk rotor, as an ultimate product, corresponding to a sliding surface with respect to a pad, is an exposed portion of the pre-form. That is, wear resistance is improved by the pre-form, which moreover plays the role of a reinforcement to increase the mechanical strength of the disk rotor in its entirety.
In manufacturing such disk rotor, it is necessary to support and secure the pre-form at a preset site of the metal mold and to maintain the supporting state even during the time of charging the molten metal. Among the techniques of maintaining the supporting state in this manner, there are a technique disclosed in JP Patent Kokai JP-A-1-272725 (first technique) and a technique disclosed in JP Patent Kokai JP-A-63-56347 (second technique). The first technique sets a molded fiber product (pre-form) by compacting and fitting it against a metal mold to prevent misregistration. The second technique applies a coating agent on the surface of a sand core and mounts a shaped fiber product (pre-form) on the sand core when the coating agent applied is as yet in a semi-dried state.
When the first technique is applied to the manufacture of the disk rotor, the pre-form is fitted and secured to the metal mold in a compressed state, so that there is raised a risk that the pre-form cannot withstand the compression stress and thus is fractured. When the second technique is applied, a separate working step is required, thus lowering the working efficiency.